1. Field of the Invention
The present invention relates to a multi stage type flow rate switching device. More particularly, the present invention relates to a multi stage type flow rate switching device suitable for controlling variably a small flow rate by being connected to a ballooned liquid medicine continuous injector (an injector where liquid medicine is filled in a balloon made of an elastic rubber material and liquid medicine is continuously injected over a period of many hours into a human body by utilizing the force produced by contraction of the balloon) that is used as a means for continuously administering a liquid analgetic, anesthetic, antibiotic, or carcinostatic agent into blood vessels, hypodermic portions, epidural portions or the like in a small amount.
2. Description of Related Art
With respect to a variable small flow rate control device used in a ballooned liquid medicine continuous injector, a device comprising flow rate control tubes connected to a multi-way stopcock has already been proposed (Japanese Unexamined Patent Publication No. JP-A-5-84310). The device is constituted by a main body having a cylindrical valve chamber where one flow inlet port and at least three flow outlet ports are formed. A plug having a cylindrical valve portion is rotatably inserted into the valve chamber of the main body. A slit opened in a fan-like shape and slender holes in a straight tube shape extending opposedly in a radial direction from the base of the slit are formed at the valve portion and, even if the slender holes of the valve portion are connected to any of the flow outlet ports, the slit is connected to the flow inlet port.
However, according to the above-described flow rate control device, one flow rate control tube is necessary for each flow outlet port and various sizes of the flow rate control tubes are necessary. It is troublesome in view of production control and assembly operation to fabricate various sizes of flow rate control tubes and integrate them simultaneously. Also, the use thereof involves a drawback where the switch angle of the lever is decreased for a large number of switchings and the display is complicated whereby erroneous operation is liable to occur.
The present invention has been achieved as a result of an intensive study in view of the above-described situation and it is an object of the present invention to provide a multi stage type flow rate switching device which simplifies production steps, which can be fabricated at a low cost and which simplifies switching of flow paths and rarely causes erroneous operation.